DNA Deoxyribose Nucleic Acid

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DNADeoxyribose Nucleic Acid
The Thread of Life
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DNA

• DNA is a double helix.
• A bonds to T C bonds to G
• In man, the DNA molecule , if fully extended,
  would have a total length of 1.7 metres. If you
  unwrap all the DNA you have in all your cells,
  you could reach the moon ...6000 times!

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DNA

• DNA STRUCTURE
• DNA REPLICATION

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Components of DNA

• NUCLEOTIDE
• Phosphate group-phosphodiester bond
• 5-Carbon sugar-deoxyribose
• nucleic acid (1 of the nucleic acids)
• Guanine-Purine
• Cytosine-Pyrimidines
• Adenine-Purine
• Thymine-Pyrimidines
• Held by hydrogen bonds
• One end of chain with free 5 phosphate group
• Other end of chain with free 3 hydroxyl group
• Adenine, thymine form two bonds
• Guanine, cytosine form three bonds

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COMPONENTS
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DNA Replication

• DNA is opened by enzymes (unzips) helicase
• Complementary nucleotides bond with the old
  strands-
• 2 strands created ½ is the old strand ½ is the
  new strand.

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DNA REPLICATION

• TAKES PLACE IN THE NUCLEUS
• END PRODUCT IS TWO IDENTICAL STRANDS
• DURING CELL DIVISION- ONE STRAND
• FOR EACH CELL
• Replication occurs only in 5(P) to 3(OH)
  direction(DNA IS READ 3 to 5)
• a. Replication of leading strand, 3' to 5' strand
• 1. New strand grows from 5' to 3end
• 2. Elongates towards replication fork

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REPLICATION
ENZYMES Helicase DNA polymerase Topoisomerase RNA
primer ligase
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From Genotype to Phenotype

• Protein synthesis--converting the genetic code
  (in DNA) into proteins that the body uses
• 3 Steps involved
• Transcription
• RNA splicing
• Translation

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DNA----RNA

• DNA
• DOUBLE STRANDED
• DEOXYRIBOSE
• NUCLEIC BASES
• THYMINE
• GUANINE
• ADENINE
• CYTOSINE

• RNA
• SINGLE STRANDED
• RIBOSE
• NUCLEIC BASES
• URACIL
• GUANINE
• ADENINE
• CYTOSINE

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• RNA
• Differences from DNA
• Single stranded (vs. Double stranded DNA)
• Contains uracil in place of thymine
• Ribose sugar (instead of deoxyribose)
• 4 Types of RNA
• preMRNA---transcribes the message from the
  DNA(rough blueprint)
• mRNA (messenger RNA)-carries message to to
  ribosome(final blueprint)
• rRNA (ribosomal RNA)--makes up the
  ribosome(forman that assembles parts of protein
  in a specific order)
• tRNA(transfer RNA)--carries amino acids to
  ribosomes

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tRNA

• Anticodon of MRNA
• Wobble to take in all possible aa combinations of
  3 nitrogen bases
• Carries specific aa on 3 on of strand

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DNA TRANSCRIPTIONDNA- GIVES CODE TO preRNA or
hnRNA
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PROCESSING
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RIBOSOME STRUCTURE

• A site - attracts Trna
• P site - forms peptide bonds between aa of
  protein
• E site - where Trns leave ribosome and aa chain
  elongates
• 5 end with initiator sequence attaches to small
  subunit
• Large subunit goes over small at the A site.
• Attracts 1st Trna with aa Met

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DNA TRANSLATIONtRNA translates mRNA into proteins
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SUMMARY
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Comparison of DNA and RNA

• RNA is single stranded
• RNA has uracil instead of thymine
• A-U

• DNA is double stranded
• DNA has thymine instead of uracil
• A-T

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Understanding DNA

• Inheritance/ Genetic Counseling
• Cell function/protein synthesis
• Embryonic development/gene regulation
• Evolution/ phylogenetic relationships
• Medicine/genetic diseases
• Genetic engineering/ recombinant DNA

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Changes in Chromosomes

• Mutation--a change in the sequence of DNA
  nucleotides (nitrogen bases)
• Causes a change in the protein formed
• Causes a change in organisms phenotype (trait)
• Effects of mutations?
• Some have little or no effect
• A few are beneficial
• Most are harmful or lethal (fatal)

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Chromosomal Mutations

• Deletion mutation--piece of chromosome breaks off
  and is lost the new DNA strands are also missing
  a piece
• Duplication--piece of chromosome breaks off and
  is inserted on homologous chromosome
• Translocation--piece of chromosome breaks off and
  attaches to a different, non-homologous
  chromosome
• Inversion--piece of chromosome breaks off, turns
  around and reattaches in opposite direction

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Mutations Illustrated
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Gene mutations

• Frameshift mutation--deletion or addition of
  single (or few) nucleotides alters the amino acid
  sequence of the protein
• Point (Substitution) mutation--wrong base is
  added in a position--new DNA chains will show the
  change

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Point Mutations
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MUTATIONS
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Frameshift Mutations

• Expansions are responsible for many genetic
  diseases
• Muscular Dystrophy (CTG repeats)
• Huntingtons (CAG repeats)
• Fragile X (CCG repeats)

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Replication Errors and Mutations

• Inheritance of mutations
• Harmful mutations
• Individuals may not live to reproductive age
• Individuals may not develop/adapt as well
• Advantageous mutations
• Help survival of organism and are passed down if
  mutation occurred in cells that produce gametes

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Genes and cancer

• Cancer is uncontrolled, abnormal cell division
• Apoptosis--programmed cell death, which is
  necessary for normal functioning
• Cause of cancer?
• Genes that control production of new cells dont
  turn off

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Genetic causes of cancer

• Oncogenes--cause cell to become cancerous
• Genes become oncogenes in 3 ways
• Mutation can occur in a growth-factor gene,
  causing rapid, uncontrolled cell growth
• Error in DNA replication, producing multiple
  copies of a single-growth factor gene
• Change in genes location--falls under the
  control of a different promoter is transcribed
  more often (producing more growth-factor)

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Tumor suppression

• Humans have tumor-suppressor genes which are
  natural anti-oncogenes
• If tumor suppressor gene is mutated, uncontrolled
  growth/reproduction occurs
• Retinoblastoma--inheritable cancer in eyes caused
  by changes in tumor-suppressor gene on chromosome
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• Can also occur when mutations occur in an
  individual (not always inherited)
• Identifying location of these genes can increase
  identification and treatment of cancer